What are essential oils?
Concentrated plant extracts
Essential oils are aromatic mixtures extracted from plants, including their flowers, leaves, bark, and fruit peels. They contain chemicals responsible for characteristic odors and flavors: the plant’s “essence.” Lavender, peppermint, and lemon oils are familiar examples. Their use in aromatherapy involves inhaling their aromas or applying diluted preparations to the skin.[1,2]
The word volatile describes a defining property of essential oils: their components readily enter the air, allowing us to smell them. Although called oils, they are chemically different from fatty oils used in food. An essential oil is also a mixture rather than a single substance, so its effects depend on the chemicals it contains.[3]
A brief history
Rene-Maurice Gattefosse People were making scented preparations thousands of years before modern aromatherapy. An Egyptian relief dated to approximately 2051–2030 BCE, now in the Metropolitan Museum of Art, appears to show perfume being pressed from flowers soaked in oil. This is evidence of an early method of capturing plant fragrance, although an infused perfume is a different preparation from a distilled essential oil.[8,4]
The history of essential oils is also a history of extraction technology. A University of Florida account notes that early distillation of aromatic plants likely focused on scented waters, with the separated oil sometimes discarded. During the seventeenth and eighteenth centuries, apothecaries refined distillation methods and studied the oils they produced. By the nineteenth century, essential oils had established uses in medicine, perfumery, and food and beverage flavoring.[9]
The term aromatherapy emerged much later. French chemist and perfumer René-Maurice Gattefossé introduced the term and published a book on the subject in 1937. His work helped frame the use of essential oils as a distinct practice, rather than simply one part of perfumery or herbal medicine.[3]
Interest expanded again during the later twentieth century, including through the work of French physician Jean Valnet. During the 1980s and 1990s, aromatherapy gained a wider following. Its modern history therefore brings together several traditions: the use of aromatic plants, the craft of distillation, and the study of fragrance and human experience.[3,9]
How they are produced
Many essential oils are obtained through steam distillation. Steam carries volatile substances out of plant material; cooling then condenses the vapor into liquid, from which the oil is separated. Citrus oils can also be obtained by mechanically pressing the peel. These methods extract a particular fraction of the plant, rather than all its constituents.[3,4]
This distinction matters when comparing an essential oil with another botanical preparation. A solvent extract can contain a broader range of substances than a distilled oil. Heat during distillation can also change some compounds. Consequently, an essential oil should not be assumed to have exactly the same composition as the plant from which it came.[4]
What is inside the bottle?
Essential oils contain varying combinations of compounds, many belonging to a chemical family called terpenes and their derivatives. Other constituents include alcohols, esters, aldehydes, and phenols. An oil may contain many individual chemicals, with a few making up a large proportion of the mixture. Its biological activity therefore reflects its composition, rather than its plant name alone.[5]
Composition is not necessarily identical between batches. Plant genetics, growing conditions, harvest timing, and extraction methods can influence the resulting oil. Even plants classified within the same species can produce oils with different chemical profiles. This variability is relevant to research: results obtained with one preparation may not apply directly to another sold under a similar name.[3,5]
How essential oils are used
Essential oils serve as fragrance and flavor ingredients in products such as perfumes, cosmetics, and foods. Aromatherapy is a separate use: it employs essential oils as a complementary health approach, commonly through inhalation or diluted skin application. Massage preparations typically mix the essential oil with a carrier oil, which acts as the diluting base.[2,3,6]
References
- National Cancer Institute. Essential oil: definition.
- National Center for Complementary and Integrative Health. Aromatherapy.
- National Cancer Institute. Aromatherapy With Essential Oils (PDQ®)—Health Professional Version.
- Sadgrove NJ, Padilla-González GF, Phumthum M. (2022). Fundamental Chemistry of Essential Oils and Volatile Organic Compounds, Methods of Analysis and Authentication. Plants, 11(6), 789.
- Dhifi W, Bellili S, Jazi S, Bahloul N, Mnif W. (2016). Essential Oils’ Chemical Characterization and Investigation of Some Biological Activities: A Critical Review. Medicines, 3(4), 25.
- National Capital Poison Center. Essential oils: Poisonous when misused.
- U.S. Food and Drug Administration. Aromatherapy.
- The Metropolitan Museum of Art. Relief fragment of a perfume press. Middle Kingdom, ca. 2051–2030 BCE.
- Pearlstine EV. (2011). Distillation of Essential Oils. University of Florida, IFAS Extension, WEC310.